This disclosure relates to motors, and more particularly, to a device for disconnecting a neutral point of a motor.
An electric machine with a xe2x80x9cYxe2x80x9d connection, such as for example one comprising a motor with three inductive phase-windings, typically has a neutral point or terminal. For a brushless permanent magnet (xe2x80x9cPMxe2x80x9d) motor, the stator is wired to the neutral point while a complimentary rotor is not so wired. During ordinary operation, the neutral point is electrically connected to the three legs of the xe2x80x9cYxe2x80x9d connection. However, under certain conditions, such as for example in a 12-Volt Electric Power Steering (xe2x80x9cEPSxe2x80x9d) system, a mechanical relay is used to open or disconnect a xe2x80x9cYxe2x80x9d connection of a motor in certain modes in order to disconnect the neutral point. Typically, a mechanical relay is used to open the neutral point because of the desirably low voltage drop across its contacts. Unfortunately, mechanical relays are undesirably large, as well as costly to operate. Typical semiconductor devices are unsuitable replacements for the mechanical relay at lower voltages because of the inefficient higher voltage drop across their terminals. Therefore, it is desirable to have a smaller, more efficient and less costly alternative.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a circuit for disconnecting a neutral point in an electric machine that includes an inductance; a three-terminal solid-state switch that has a first terminal connected to the inductance, a second terminal connected to the neutral point, and a third terminal for controlling a flow of current between the first and second terminals; a controlling circuit coupled to the three-terminal solid-state switch that includes a first loop that has a power source, a resistance, and a voltage regulator to maintain a first voltage upon the third terminal and cause the three-terminal solid-state switch to switch on to thereby electrically connect the first terminal to the second terminal, and a second loop that has a resistance, a power source, and a trigger switch being controllably switched closed to thereby close the second loop to apply a second voltage to the third terminal, thereby causing the three-terminal solid-state switch to switch off to electrically disconnect the first terminal from the second terminal.